This invention relates generally to radiographic inspection systems, and more particularly to a method of operating a radiographic source with a fixed anode.
X-ray tubes produce X-rays by accelerating electrons into a tungsten or other dense target. During this process, as much as 99 percent of the tube's electrical energy becomes thermal energy. Ideally an x-ray tube would produce a large x-ray output flux from a very small x-ray focal spot to produce high quality images in a short period of time. Unfortunately, these two requirements compete. Inspection time and spot cooling capability are directly related to the X-ray output, which is directly related to the focal spot size. However, focal spot size is inversely related to image resolution. Therefore, trade-offs must be made between tube life, inspection speed, and image quality.
Prior art fixed anode X-ray tubes provide moderate focal spot sizes with relatively low output flux. They offer a low cost, high reliability source of x-rays for continuous use in radiographic inspections. Rotating anode tubes move a metallic target in front of a fixed electron beam, increasing the effective target cooling area and permitting improved tube output while maintaining focal spot size. This requires a mechanism to rotate the anode while maintaining anode cooling and tube vacuum. These requirements generally increase tube cost and reduce tube life when compared to fixed anode tubes.
Accordingly, there is a need for a method of operating a fixed anode X-ray inspection system to increase cooling capability while maintaining a small focal spot size.